Influence of Ni Schottky contact thickness on two-dimensional electron-gas sheet carrier concentration of strained Al0.3Ga0.7N/GaN heterostructures

Ni/Au Schottky contacts with thicknesses of either 50 angstrom/50 angstrom or 600 angstrom/ 2000 angstrom were deposited on strained Al (0.3) Ga (0 .7) N/GaN heterostructures. Using the measured C-V curves and I-V characteristics at room temperature, the calculated density of the two-dimensional electron-gas (2DEG) of the 600 angstrom/2000 angstrom thick Ni/Au Schottky contact is about 9.13 x 10(-12) cm(-2) and that of the 50 angstrom/50 A thick Ni/Au Schottky contact is only about 4.77 x 10(-12) cm(-2). The saturated current increases from 60.88 to 86.34 mA at a bias of 20 V as the thickness of the Ni/Au Schottky contact increases from 50 angstrom/50 angstrom to 600 angstrom/2000 angstrom. By self-consistently solving Schrodinger's and Poisson's equations, the polarization charge sheet density of the two samples was calculated, and the calculated results show that the polarization in the AlGaN barrier layer for the thick Ni/Au Schottky contact is stronger than the thin one. Thus, we attribute the results to the increased biaxial tensile stress in the Al-0.3 Ga-0.7 N barrier layer induced by the 600 angstrom/2000 angstrom thick Ni/Au Schottky contact.